One marine was killed and three others seriously injured in an explosion in Bacho district of Narathiwat province on Thursday morning, police said.
The incident occurred at 7.05am on Highway 42, the Narathiwat-Pattani route, at Ban Sompoy in tambon Kayomati.
As the pickup truck with eight marines from a base in Ban Sompoy was passing in front of a village mosque, militants hiding on the roadside remotely detonated a bomb hidden in a garbage can.
Following the explosion, the marines, who were on patrol to provide security for teachers travelling to school, returned fire. The militants withdrew after a five-minute firefight.
Pvt Kittipong Butsripa, 23, was killed in the explosion. Three others were wounded: Warrant Officer Somchai Thopsee, 40, the patrol leader, Pvt Paskorn Boonmaporn, 22, and Pvt Nirut Khumpong, 23.
The wounded were admitted to Bacho Hospital and later transferred to Narathiwat Ratchanakarin Hospital.
A naval bomb-disposal team was dispatched to the scene for examination. The bomb was found to be made of a 25kg gas cylinder wired to a communication radio.
About 50 spent shells of M16 and AK47 rifles were found at the scene.
Authorities believed the attack was the work of a group of militants led by Romuelee Kachaekaso which operated in Bacho district.